Electronic equipment, notably memories are often used in environments where they are or may be subjected to high energy particles. They may also be subjected to a high energy electromagnetic pulse field. Such particles may include alpha, beta, gamma and other particles which have sufficient energy to pass through the outer surface of a plastic case and impact the memory cell itself.
Outer space is one environment in which a memory cell would be subjected to impact from a high energy particle. When the sun has an energy eruption, which occurs with increasing frequency and intensity during high activity sunspot cycles, the likelihood of impact of a high energy particle on objects orbiting the Earth becomes extremely high. Other environments, such as a nuclear explosion or a lightning strike may also produce high energy particles or a high energy electromagnetic pulse (EMP).
Many integrated memory circuits in use today have a reverse biased PN junction that will be shorted due to charges generated by the high energy particle hit. If this happens to a standard memory cell, the logic state of the cell becomes unknown. It may be inverted, or the data may be erased. Accordingly, current memory cells must either be protected from high energy particle hit, or on the other hand designed in such way that they are resistant to a change in data state even if hit by a high energy particle or exposed to a high energy EMP.